In a wireless communication system, mutual interference exists between signals of different users, and in a Gaussian interference channel, each user knows respective complete channel information, but data of different users cannot be shared, so joint transmission cannot be performed. FIG. 1 shows a two-user Gaussian interference channel, in which interference exists between the users x1 and x2. How to improve the capacity of the Gaussian interference channel while eliminating the interference between the users is always one of main bottlenecks limiting the development of the technology.
With deep research into the Gaussian interference channel, a method for cancelling interference between users by using interference alignment is proposed. In interference alignment, in the case that complete channel information is known, useful signals and interference signals of each receiving end are spatially separated by preprocessing at a transmitting end, and all interference with the receiving end caused by different transmitting ends is aligned to the same spatial dimension. In this way, the impact caused by the interference is prevented, and the capacity is improved.
To prevent interference between users, data may be transmitted in a TDMA mode shown in FIG. 2. That is, users transmit data at different time points. This prevents the interference between users. Compared with the system suffering from mutual interference in the case of simultaneous transmission by multiple users, the performance of TDMA is superior to that of the multi-user interference system. It can be seen from the schematic diagram that TDMA is capable of effectively preventing interference between users. Similar to TDMA, FDMA enables different users to transmit data at different frequencies, which also prevents the interference between users.
The prior art proposes a method for interference alignment on a special channel, as shown in FIG. 3. K transmitting ends and K receiving ends exist, the channel response from each transmitting end to a destination receiving end is 1, and the interference channel response of each transmitting end to all users is i. If it is assumed that a transmit signal is a real part of a signal space, a receive signal of the kth receiving end is:
      r    k    =            s              k        ⁢                                        +          i      ⁢                        ∑                                    l              =              1                        ,                          l              ≠              K                                K                ⁢                  s          l                      +          n      k      
The above formula reveals that the receiving end can detect the transmit signal only by directly taking the real part of the receive signal, that is,
      Re    ⁡          (              r        k            )        =            Re      (                        s                      k            ⁢                                                                +                  i          ⁢                                    ∑                                                l                  =                  1                                ,                                  l                  ≠                  K                                            K                        ⁢                          s              l                                      +                  n          k                    )        =          Re      ⁡              (                              s            k                    +                      n            k                          )            
Obviously, the signal space of the transmit signal is half consumed to eliminate the interference between users. The channel capacity of a single user may reach ½ log(SNR)+o(log(SNR)). When the number of users is greater than 2, the system achieves a greater gain over the original system capacity.
During the implementation of the present invention, the inventor discovers at least the following problems in the prior art.
The data transmitted in the TDMA mode is capable of avoiding interference, which, however, results in a low system capacity. The interference alignment on the special channel is difficult to construct in practice and therefore cannot be applied on an actual channel.